Recently, vehicles that are propelled by the drive power of an electric motor, such as electric vehicles (EV), hybrid vehicles (HEV), plug-in hybrid vehicles (PHEV), and fuel cell vehicles (FCV), have incorporated therein a plurality of chargeable and dischargeable secondary cells, which are connected in series and stored as a battery module (battery assembly) in a battery box. The battery module generates a high DC voltage for energizing an electric motor through a motor-energizing inverter.
The voltage, which represents a remaining stored energy level of each cell of the battery module, is monitored at all times by a voltage monitoring circuit.
According to “GUIDELINES FOR ELECTRIC VEHICLE SAFETY-SAE J2344 JUN 1998 (4.3.2.1 Suggested Disconnect Location and Type),” a manual switch (manual disconnect) is required to be added in the vicinity of a midpoint where the voltage of a battery module, which is made up of an array of series-connected cells, is divided into two voltages. When the manual switch is opened, the DC voltage of the battery module is lowered.
There is known an arrangement in which a fuse is integrally combined with a current blocking switch. See, FIG. 1 of Japanese Laid-Open Patent Publication No. 10-083753.
One type of storage battery for use as a battery assembly has contacts, which are opened to cut off an electric current in the event of an undue pressure buildup in the battery, due to gas generated by decomposition of the electrolyte upon overcharging of the battery. See, FIGS. 2 and 4 of Japanese Laid-Open Patent Publication No. 2005-044523, (hereinafter referred to as JP2005-044523A).
According to a known voltage monitoring circuit, the positive and negative terminals of series-connected cells and the voltage monitoring circuit are connected by a number of wires. Differential amplifiers (operational amplifiers) of the voltage monitoring circuit detect voltages of the cells for monitoring the voltages at all times. See, for example, paragraph [0021] and FIG. 1 of Japanese Laid-Open Patent Publication No. 2005-292137 (hereinafter referred to as JP2005-292137A).
If the aforementioned current blocking switch is connected in series to the battery module, then when the current blocking switch is closed, the voltage across each cell is input to the voltage monitoring circuit, which detects the voltage across each cell.